Volume control circuits



Jan. 14, 1941. B. e. BJORNSON VOLUME CONTROL CIRCUITS Filed Oct. 11, 1939 INVEN TOR .8. G. BJORNSON ATTORNEY Patented Jan. 14, 1941 VOLUME CONTROL CIRCUITS Bjorn G. Bjornson, New York, N. Y., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application October 11, 1939, Serial No. 298,888

16 Claims.

This invention relates to volume control circuits and particularly to volume control circuits for maintaining speech signals at constant volume.

One object of the invention is to provide volume control circuits that shall weigh the time a given voltage is exceeded and the number of syllables on a transmission line in an improved manner for controlling the volume of the speech signals.

Another object of the invention is to provide volume control circuits that shall maintain a constant relation between the time a given voltage is exceeded on a signal transmission line and the number of syllables.

Another object of the invention is to provide volume control circuits that shall weigh the time a given voltage is exceeded and the number of syllables for controlling the volume on a transmission line and that shall maintain the rate of gain change constant.

A further object of the invention is to provide volume control circuits having a control condenser for governing the speech volume on a transmission line according to the charge thereon that shall impress a variable charging potential on the control condenser according to the time a given voltage is exceeded and the number of syllables which is high relative to the charge on the condenser to maintain an even rate of gain change.

In transmitting signals, for example, speech signals over certain types of transmission systems it is desirable to hold the signals at substantially constant volume. It is desirable in the Transatlantic Radio System to hold the speech signals at constant volume in order to prevent overloading of the apparatus in the transmitter. The Volume range between a very loud talker and a very Weak talker may be such as to cause overloading of the apparatus in the radio transmitter by the strong talker when the weak talker is raised tov a satisfactory level. In order to prevent overloading the apparatus in the radio transmitter, the signal currents produced by the weak talker and the strong talker are controlled by a voice-operated gain adjusting device so that constant volume is supplied to the radio transmitter.

The volume control circuits disclosed are an improvement on the volume control circuits disclosed in the application of B. G. Bjornson Serial No. 298,887 filed October 11, 1939. In volume control circuits of the type under consideration, the time a given voltage is exceeded and the number of syllables in speech signals are weighed against each other and proper balance obtained which can be employed to adjust the strengths of the speech signals.

In the circuits employed to describe the invention a vario-losser comprising series and parallelly arranged resistance elements is inserted in a signal transmission line for controlling the strength or amplitudes of the speech signals. The resistance elements in the vario-losser preferably are in the form of copper oxide rectifier elements having non-linear resistance current characteristics. A bridge circuit having one arm in the form of a gain control tube is provided for governing the resistance value of the resistance elements in the vario-losser. The gain control tube is governed according to the ratio of the time a given voltage is exceeded and the number of syllables on the signal transmission line. When no signals are on the transmission line the vario-losser has a resistance value to obtain a mean gain on the transmission line.

A syllabic amplifier detector circuit which is connected to the transmission line before the vario-losser is provided with means whereby it may be operated by signals above a certain value. The syllabic detector circuit includes a pulser device Which is operated by low strength syllabic impulses. Means are provided whereby the pulsing device is only operated on the rising portion of a syllabic impulse. Means are also provided whereby the pulser device operates for a predetermined time irrespective of the strength or duration of a syllabic impulse. The pulser device operates a driver circuit for supplying spurts of low frequency alternating current to operate a syllabic cold-cathode detector tube. A high strength cold cathode detector tube is connected to the transmission line beyond the vario-losser by means of a hybrid coil.

The two detector tubes are each of the threeelement type having an ignition circuit and an operating circuit. The ignition circuits are broken down by the syllabic detector circuit and the backward acting circuit connected to the hybrid coil. The operating circuits for the two detector tubes are supplied with current from ,a low frequency alternating current source so that the tWo tubes receive opposite half-waves. Thus thetwo detector tubes operate degrees out of phase with, respect to each other. Two cold cathode balancing tubes are respectively broken 'down bythe two detector tubes for charging a balancing condenser to weigh the operations of the two detector tubes. The balancing condenser is charged in one direction or the other according to which detector tube predominates in the control thereof. No means is provided for ,blockingthe syllabic detector circuit when the backward acting circuit controlling the high frequency detector tube is in operation because the .two detector tubes do not operate in phase with each other. Resistance means is provided in the operating circuit of the high strength detector tube to compensate any effect on the balancing .condenserthat may be made by the syllabic detector tube. The detector tubes respectively ignite two enabler tubes when operated. The enabler tube ignited by the syllabic detector tube may be called the gain increaser tube and the enabler tube operated by the high strength detector tube may be called the gain decreaser tube. The gain increaser tube and the gain decreaser tube, respectively, operate in phase with the syllabic detector tube and the high strength detector tube.

The balancing condenser impresses positive or negative potential on the grid of a gain rate control tube which in turn controls a driver arrangement having two separate paths. An output transformer connected to the driver arrangement has two primary windings respectively associated with the two paths. The secondary winding is connected to the operating circuits of the gain increaser tube and the gain decreaser tube. The two primary windings of the output transformer are wound oppositely so that when equal currents flow through the two paths no current will be supplied to the secondary winding of the output transformer. An input transformer connected to a source of low frequency alternating current is provided for supplying the two paths with a low frequency current. The gain rate control tube varies the resistance value of resistance elements in the two paths so that the current flow through one or the other of the paths predominates according to whether low strength signals or high strength signals are on the transmission line.

The gain control tube is governed by the driver arrangement according to Whether the output therefrom is above a certain value and in phase with the gain increaser tube or the gain decreaser tube. If the driver arrangement output is above a certain value and in phase with the gain increaser tube the gain control tube is operated to raise the gain in the transmission line. If the driver arrangement output is above a certain value and in phase withthe gain decreaser tube, then the gain control tube is operated to lower the gain in the transmission line. isolator tube of the cold cathode type is provided for preventing any change in the gain on the transmission line until the output from the driver arrangement is raised above a predetermined point.

The single figure in the accompanying drawing is a diagrammatic view of a system constructed in accordance with the invention;

Referring to the drawing, a gain control station I is shown comprising a vario-losser 2 and two space discharge amplifier tubes 3 and 4. Input conductors 5 and 6 are connected to the variolosser 2 by means of a transformer I and output conductors 8 and 9 are connected to the amplifier tube 4 by means of a hybrid coil I0 and a transformer I. The vario-losser 2 is connected to the amplifier tube 3 by means of a transformer l2. The transformer I2 is provided with a secondary winding l3 and two primary windings l4 and IS. The transformer l which connects the variolosser to the input conductors 5 and 6 is provided with two secondary windings l6 and H. Four series arranged resistance elements l8, I9, 20 and 2| in the form of copper-oxide rectifiers are positioned between the transformers 1 and I2 and are respectively shunted by resistance elements 22, 23, 24 and 25. Shunt resistance elements 26, 21, 28 and 29 in the form of copperoxide rectifier elements are connected between the elements l8 and 2| and the elements I9 and 20. A condenser 30 provides low alternating cur- A marginal I rent impedance between a tap from the secondary windings I6 and ll of the transformer I and a tap from the primary windings l4 and I5 of the transformer I2.

The amplifier tube 3 and the feedback amplifier tube 4 perform no special function in the operation of the circuits other than that of the amplification and a detailed description of these parts is deemed unnecessary.

Two contact members 3| and 32 on the variolosser 2 are connected to opposite vertices on the bridge circuit 33. The bridge circuit comprises three resistance arms 34, 35, and 36 and the space current path of a three-element tube 31. The tube 31 which may be designated as the gain control tube varies the bridge 33 to control the variolosser 2. Battery 38 is connected to the other two vertices of the bridge 33. The gain control tube 31 is governed according to the strength of the signals on the transmission line for governing the bridge 33 which in turn controls the potentials impressed on the contact members 3| and 32 of the vario-losser 2. If positive potential is impressed on the contact member 32 and negative potential is impressed on the contact member 3| the vario-losser has low loss to increase the gain on the transmission line. If the contact member 32 has negative potential impressed on it and the contact member 3| has positive potential impressed on it the resistance value of the vario- -losser will be increased to lower the gain on the transmission line.

Assume positive potential is impressed on the contact member 32, a circuit is completed from the terminal 32 through the secondary winding I4, resistance elements l8 and I8 and the primary winding IE to the contact member 3|. A second circuit is completed from the contact member 32 through secondary winding l5, resistance elements 20 and 2| and the primary winding H to the contact member 3|. A third circuit is completed from the contact member 32 through the resistance elements 21 and 26 to the contact member 3|. A fourth circuit is completed from the contact member 32 through the resistance elements 28 and 29 to the contact member 3 In the circuits above traced it may be noted that the series resistance elements I 8, I9, 28 and 2| have current flow therethrough in a direction to reduce the resistance values greatly whereas the parallel resistance elements 26, 21, 28 and 29 have very little current flow therethrough, accordingly their resistance values are reduced very little. Thus the parallel resistance elements have great resistance value and the series resistance elements have little resistance value so that the opposition to current flow by the vario-losser is greatly reduced. An opposite effect takes place in case negative potential is impressed on contact member 32 and positive potential is impressed on contact member 3|. In the latter case the resistance values of the parallel to shunt resistance elements 26, 21, 28 and 29 are reduced greatly, whereas the resistance values of the series elements I8. I9 20 and 2| are changed very little.

A syllabic detector circuit 39 which is connected to the input conductors 5 and 6 before the vario-losser 2 is provided for igniting a syllabic detector tube 40. The syllabic detector circuit comprises a pentode amplifier 4|, a diode triode 42, a pulser device 43 and a driver circuit 44. The input circuit of the amplifier tube 4| is connected to the input conductors 5 and 8 by means of a transformer 45. Two condensers 46a and 41a are associated with the transformer 45 to form a band-pass filter which passes frequencies having a center about 1200 cycles. The output circuit' of the amplifier tube 4| is connected by the transformer 46 to the diode of the diode-triode 42. A condenser 41 is associated with the transformer 46 for tuning the same to a frequency of approximately 1000-cycles. The diode-triode device 42 comprises an anode 48, a control grid 49, a cathode 59 and auxiliary anode 5|. The filament for heating the cathode 5|] is energized by a battery 52. The circuit for heating the filament may be traced from the battery 52 through the filament, resistance element 53 and resistance element 54 to the battery 52. The drop across the resistance element 53 is employed to impress a negative bias on the grid 49. In order to provide a normal bias on the grid 49 without changing the circuit of the diode, the resistance elements 53 and 54 are symmetrically placed with respect to the diode circuit and the bias taken across the resistance element 53.

The diode circuit which is connected to the secondary winding of the transformer 46 may be traced from one terminal of the secondary winding through the auxiliary anode 5|, cathode 5U, resistance element 53 and resistance elements 55 and 56 to the other terminal of the secondary winding. A condenser 51 and two resistance elements 58 and 54 are connected in shunt to the resistance elements 53, 55 and 56. The resistance element 58 is equal in value to the resistance elements 55 and 56. The resistance element 53 is equal in value to the resistance element 54. The potential dropv across the resistance elements 53 and 55 when varied by the signals on the transmission line is employed for inserting a variable negative bias on the control grid 49 of the triode portion. The triode portion of the diode-triode normally has only a small negative potential impresed on the grid 49 so that space current flows through the tube. When signals are on the transmission line the negative potential impressed on the grid 49 is increased and in case of very strong signals the triode portion of the diode triode will be blocked so that the syllabic detector circuit 39 is rendered inoperative.

The triode portion of the diode triode 42 is connected by a transformer 59 to the pulser device 43. The condenser 69a. in the circuit of the primary Winding of the transformer 59 tunes the transformer to a syllabic frequency. Preferably the transformer is tuned to a frequency between 6 and 8 cycles. The secondary winding for the transformer 59 has a copper-oxide rectifier element 6| in shunt therewith so that the pulser device 43 can only be operated on the rising portion of a syllabic impulse. The copper-oxide elements 66 in'series with the secondary winding of transformer 59 prevent the impedance changes of the diode-triode from affecting the characteristic of the pulser device 43 excessively.

The pulser device 43 comprises an upper element having a control grid 62, an anode 63 and a cathode 64, and a lower device having an anode 65, control grid 66 and the cathode 64. Two condensers 61' and 68 and two resistance elements 69 and 10 are provided for governing the operation of the pulser device as will be explained later.

The driver circuit 44 comprises a transformer 1|, connected to a source 12 of low frequency alternating current. The secondary winding of the transformer 1| is connected through resistance elements 13 to a transformer 14. The secondary winding of the transformer 14 is connected to the ignition circuit of the low strength detector tube 46. The resistance elements 13 are preferably composed of silicon carbide and a binder material. Elements of this type are disclosed in the patent to K. B. McEachron 1,822,742, dated September 8, 1931. Resistance elements 15 of the same type as the resistance elements 13 are connected across the connection between elements 13 and the primary winding of the transformer 14. A battery 16 is connected to a mid-point on the primary winding of the transformer 14, the anode 63 of the upper device in the pulser is connected to a mid-tap on the secondary winding of the transformer 1| and the anode 65 of the lower device of the pulser is connected to a mid-tap on the resistance elements 15. When potential is impressed on the resistance elements 13 the series impedance of the driver circuit is lowered, whereas if the potential is impressed on the resistance elements 15 the shunt impedance of the driver circuit is increased.

Normally when the pulser device 43 is not operated the lower device is energized and the condenser 68 is charged. The output circuit of the lower device may be traced from the battery 16 to the mid-tap of the primary winding of the transformer 14 in parallel through the primary winding sections in parallel'through the resistance devices 15, anode 65, cathode 64, resistance 69 and ground return to the battery 16. The potential drop across the resistance element 69 is employed to impress a negative bias on the control grid 62 of the upper device in the pulser.

In case the pulser is operated by a syllabic impulse, the negative bias on the control grid 62 is reduced to permit current flow through the upper device. The output circuit of the upper device in the pulser may be traced from the grounded battery 16 to a mid-tap on the primary winding of the transformer 14, sections of the primary winding for the transformer 14, resistance elements 13 and sections of the secondary winding of the transformer 1| in parallel to the anode 63, cathode 64, resistance element 69 and ground return to the battery 16. Upon operation of the upper device in the pulser, the condenser 68 is discharged through a circuit which may be traced from one terminal of the condenser through the anode 63, cathode 64 and resistance element 11 to the other terminals of a condenser 68. The potential drop across the resistance element 11 impresses a negative bias on the control grid 66- of the lower devicein the pulser to block the lower device. Upon operation of the upper device of the pulser, the condenser 61 is charged. However, when the lower device of the pulser is blocked the charge on the condenser 61 is discharged through the resistance element 10. The discharge circuit for the condenser 61 may be traced from one terminal in the condenser through the anode 65, cathode 64, resistance element E9, and resistance element 1|] to the other terminal of the condenser 61. The potential drop across the resistance element 10 due to the discharge of the condenser 61 impresses a negative bias on the control grid 62 to block the operation of the upper device in the pulser.

The pulser device operates the driver circuit 44- to sup-ply spurts of low frequency current from the source 12 to ignite the detector tube 49. The spurts of low frequency current are the same irre-' spective of the strength or duration of the syllabic impulses which control the pulser devices. The syllabic detector tube 4|] which is operated by the syllabicdetector circuit 39- comprises electrodes a reason of the connection of the source 89 of low 7 tube 96.

I8. 19 and 80. The electrodes I9 and 80 are connected to the secondary winding of the transformer I4 in the driver circuit 44.

A high strength detector tube 8| comprising electrodes 82, 83, and 84 is ignited by a backward acting circuit connected to the hybrid coil I0. The electrodes 83 and 84 areconnected to the hybrid coil I0 by means of a transformer 85. The operating circuit for the detector tube 40 may be traced from the electrode 80 through the secondary winding of transformer 86, resistance element 81 and resistance element 88 to the electrode I8 of the detector tube 40. The primary winding of the transformer 86 is connected to a source 89 of low frequency current which energizes the operating circuit of the detector tube. The potential drop across the resistance element 88 serves to ignite a gain increaser cold cathode 90. The potential drop across the resistance element 81 serves to break down a balancing cold-cathode tube 9| to charge a balancing condenser 92 in one direction.

The operating circuit for the high strength detector tube 8| may be traced from the electrode 84 through resistance elements 93, 94 and 95 and the secondary winding of the transformer 88 to the electrode 82 of the detector tube 8|. The potential drop across the resistance element 94 is employed to ignite the gain decreaser cold-cathode The potential drop across the resistance element 95 is employed to ignite a balancing coldcathode tube 91 to charge the balancing condenser in an opposite direction to that in which it was charged by ignition'of the tube 9|. By

frequency current to the detector tubes 40 and 8| it is apparent that the two detector tubes are operated by opposite half cycles so that the two detector tubes operate 180 degrees out of phase with respect to each other. Likewise, the gain increaser tube 90 and the gain decreaser tube 95 are ignited out of phase with respect to each other.

The balancing condenser 92 averages or weighs the operations of two detector tubes 49 and 8| to control a gain rate control tube 98. The circuit controlling the high strength detector tube 8| does not block the syllabic circuit or the detector tube 40 by reason'of the two detector tubes having operating circuits 180 degrees out of phase with respect to each other. The effect of the detector tube 40 on the balancing condenser 92 during the operation of the detector tube 8| is taken care of by the resistance elements in the operating circuit of the high strength detector tube 8|.

The potential drop across a portion of a resistance element 99 which is connected in shunt to the balancing condenser 92 serves to impress a positive or negative potential on the control grid of the gain rate control tube 98. If the syllabic detector tube 40 predominates in the charging of the balancing condenser 92 then a negative potential is impressed on the control grid of the tube 98. However, if the high strength detector tube 8| predominates in the charging of a balancing condenser 92 then a positive potential is impressed on the control grid of the tube 98.

The gain rate control tube 98 governs the operation of a driver circuit I00. The driver circuit comprises an input transformer I0| having a primary winding I02 and two secondary windings I04 and I05 and an output'transformer I06 having a secondary winding I01 and two primary windings I08and I09. The primary winding I02 of the transformer I0I is connectedto a. source I I0 of low frequency alternating current. The primary windings I08 and I09 of the transformer I06 are oppositely wound and are respectively inserted in two different paths of the driver circuit. Series resistance elements III, II2, I I3 and I I4 of the copper-oxide type are provided in circuit between the secondary'windings I04 and I05 of the transformer |0I and the primary windings I08 and I09 of the transformer I06. Resistance elements H5, H6, H1 and ||8 of the copper-oxide type are connected in shunt across the circuit between the secondary windings of the transformer I 0| and the primary windings of the transformer I06. Two contact terminals 9 and I 20 separated by condenser |2| are connected to resistance elements I22 and I23. Direct current potential is supplied to the contact members 9 and I20 of the driver circuit I00 for controlling the copper-oxide resistor elements in accordance with the operation of the gain rate control tube 98.

One terminal of each of the resistance elements I 22' and I 23 is connected to agrounded battery I24. The other terminal of the resistance element I22 is connected to the anode of the gain rate control tube 98 so that the resistance element I22 has current flow therethrough according to the operation of the tube 98. The other terminal of the resistance element I23 is connected through a resistance element I25 to the other terminal of the grounded battery I24. The potential drop across the two resistance elements I22 and I23 oppose each other and under normal conditions when no signals are being transmitted over the transmission line, no potential will be impressed between the contact members 9 and I20 of the driver circuit IIIIl.

If the detector tube 40 predominates in the operation of the balancing condenser 92 then the current flow through the gain rate control tube 98 is reduced to impress positive potential on the contact member H9 and negative potential on the contact member I20 of the driver circuit I00. If the high strength detector tube 8| predominates in controlling the balancing condenser 92, then current flow through the gain rate control tube 98 is increased to impress negative potential on the contact member I I9 and positive potential on the contact member I20 of the driver circuit I00.

When positive potential is impressed on the contact member 9 a circuit is completed from the contact member 9 through the primary .winding I09, series resistance elements III and H2 and secondary winding I04 to the contact terminal I20. The copper-oxide elements III and H2 have their resistance values greatly reduced to permit the flow of alternating current from the-transformer secondary winding I04 to the primary winding I09 of the transformer I06, A second circuit is completed from the contact member II 9 through the copper-oxide element I I 5 and the copper-oxide element I I1 to the contact member I20. The copper-oxide elements H5 and II! will have their alternating'current impedance increased due to the flow of direct current. This will increase the flow of alternating current through the winding I09. A third circuit may be traced from the contact terminal ||9 through the primary winding I08, copperoxide resistance elements 4 and H3 and sec ondary winding I05 to the contact terminal I20. In thiscircuit, the copper-oxide elements I I4 and I I3 will have their alternating current impedance increased to reduce the alternating current flow throughthe windingI08.- A fourth circuit is completed from the contact member II9 which may be traced from the contact member H9 through copper oxide element H6 and the copper-oxide element I I8 to the contact terminal The elements H6 and H8 permit the free flow of direct current through them so that the elements efiect considerable shunting action across the secondary winding I05 and the primary winding I 08. Consequently little alternating current is transmitted from the source IIO through the secondary winding I05 to the primary winding I08.

In the example above taken the primary winding I09 predominates over the primary winding 1 08 and accordingly controls the secondary winding I 01 of the transformer I06. This is always the case when the low strength detector tube 40 controls the balancing condenser 92. If the high strength detector tube 8I controls the balancing condenser 92 an opposite eflect will take place and the primary winding I08 of the transformer I06 will predominate over the primary winding I09 in controlling the secondary winding I01.

The gain increaser cold cathode tube 90 comprises three electrodes I26, I21 and I28. The electrodes I 21 and I28 are connected across the resistance element 88 by means of a transformer I29. The gain decreaser cold cathode tube 96 comprises three electrodes I30, I 3| and I32. The electrodes I3I and I32 are connected across the resistance element 94 by means of the transformer I33. The. operating circuit for the gain increaser tube 90 may be traced from the electrode I28 through secondary winding I01 of the transformer I06 and resistance element I34 to the electrode I26. The operating circuit of the gain decreaser tube 96 may be traced from the electrode I3I through secondary winding I01 of the transformer I06 and resistance element I35 to the electrode I30. The tubes 90 and 96 are ignited in phase with the detector tubes 40 and BI. Moreover, the secondary winding I01 is energized in opposite phases according to whether the primary winding I08 or the primary winding I09 predominates. Consequently, the secondary winding I01 has current therein in phase with the operation of the enabler tube 90 or the enabler tube '96.

A gain control condenser I36 is provided for controlling the potential on the grid of the gain control tube 31 according to the charge thereon. The charge on the condenser I36 is governed according to the operation of the enabler tubes .90 and 96 in combination with the driver circuit I00. If the driver circuit I00 and the enabler tube 90 are operated by the syllabic detector tube 40, then the condenser I36 is charged to impress a negative potential on the control grid of the tube 31. If the driver circuit I00 and the enabler tube 96 are controlled by the high strength detector tube 8I then the condenser I36 is charged to impress positive potential on the control grid of the gain control tube 31.

The gain control condenser I36 is connected across the resistance elements I35 and I34 in series with a marginal isolator tube I31. The isolator tube I31 is of the cold cathode type and comprises electrodes I38 and I39. The isolator tube I31 being marginal in operation prevents changing of the charge on the gain control condenser I36 until the driver circuit I00 is operated above a predetermined point. The resistance I40 is included in the filament heating circuit for the tube 31. The charge impressed on the condenser I36 'under control of the driver circuit I00 is always large with respect to the normal charge so that the same rate of gain change is effected at all times during the operation of the gain control circuits.

If low strength signals are on the transmission line the syllabic detector circuit 39 is operated for supplying spurts of low frequency alternating current from the source 12 to the low strength detector tube 40. The detector tube 40 is ignited and the operating circuit therefore breaks down and ignites the gain increaser tube 90 and the balancing tube 9|. The balancing tube 9I permits charging of the balancing condenser 92. If low strength signals predominate over high strength signals for a period of time the balancing condenser 92 operates the gain rate control tube 98 which in turn controls the driver circuit I00 to supply the secondary winding I01 of the transformer I 06 with current from the primary winding I09 which under the conditions above set forth predominates over the primary winding I08. The transformer winding I01 in combination with the gain increaser tube 90 charges the condenser I36 to reduce the current flow through the gain control tube I31. The gain control tube I31 so controls the bridge circuit 33 as to impress positive potential on the contact member 32 and negative potential on contact member 3I of the vario-losser 2. Positive potential on the contact member 32 changes the impedances of the vario-losser as above set forth to increase the gain on the transmission line.

In case high strength signals predominate on the signal transmission line, the high strength detector tube 8! effects ignition of the gain decreaser tube 96 and ignition of the balancing tube 91. The balancing tube 91 permits charging of the balancing condenser 92. The balancing condenser 92 if charged predominantly by the operation of the detector tube 8|, operates the gain rate control tube 98 to impress positivepotential on the contact member I20 and negative potential on contact member II9 of the driver circuit I00. Such operation of the driver circuit insures that the primary winding I 08 predominates over the primary winding I09. The secondary winding I01 in transformer I06, when energized by the primary winding I 08, is in phase with the gain decreaser tube 96. The gain control condenser I36 is then charged to impress positive potential on the control grid of the gain control tube I 31. The gain control tube I 31 governs the operation of the bridge 33 to impress negative potential on the contact member 32 and positive potential on the contact member 3! of the vario-losser. Such operation of the vario-losser insures a change in the impedances of the vario-losser to reduce the gain on the transmission line. If the detector tubes 40 and 0| have operated according to a predetermined ratio, constant volume may be maintained on the transmission line.

Modifications in the circuits and in the arrangement and location of parts may be made within the spirit and scope of the invention and such modifications are intended to be covered by the appended claims.

What is claimed is:

1. In combination, a signal line, gain control means for controlling the strength of the signals on said line, means comprising a control condenser for governing said control means according to the charge on the control condenser, said control means being adjusted to hold the gain at a fixed average value when no signals are on the line, and means controlled according to the ratio between the time a given voltage is exceeded and the number of syllables on the'line for charging said condenser with a potential which is high relative to the charge thereon to govern the gain control means and maintain the line signals at constant volume.

2. In combination, a signal line, a vario-losser on said'line for controlling the strength of the signals, a bridge circuit for controlling the resistance values of said vario-losser, a gain control tube having-a control grid and forming one arm of said bridge, a control condenser for im pressing a bias on said control grid according to the charge thereon, and, means controlling according to the ratio between the time a given voltage is exceeded and the number of syllables on the line for charging the control condenser to govern the gain control tube and maintain the signals at constant volume, said vario-losser being adjusted to bring the gain to a mean normal value when no signals are on the line.

3. In combination, a signal line, a vario-losser on said line for controlling the strength of the signals, two cold cathode detector tubes, means for operating said tubes respectively according to the time a given voltage is exceeded and the number of syllables on said line, balancing means for weighing the outputs from said detector tubes, and means controlled by said balancing means for governing the resistance values of said vario-losser to maintain the signals on the line at constant volume, said vario-losser being adjusted to bring the gain to a mean value when no signals are on the line.

4. In combination, a signal line, a vario-losser on said line for controlling the strength of the signals, and means controlled according to the ratio between the time a given voltage is exceeded and the number of syllables on the line for varying the resistance value of said variolosser to maintain constant volume, said variolosser being adjusted. to bring the gain to a mean value when no signals are on the line.

5. In combination, a signal line, a gain varying device for controlling the signals on said line, and means controlled according to the ratio between the time a given voltage is exceeded and the number of syllables in thesignals on the line for governing said device to control the volume of the signals on the line.

6. A signal line having a gain varying device therein, a balancing condenser, means for charging said condenser with potentials of different polarity according to the ratio between the time a given voltage is exceeded and the number of syllables in the signals on the line, and means controlled according to the polarity of the charge on said condenser when charged above a predetermined level for governing said device to maintain the signals on said line at substantially constant volume.

'7. A signal line having a gain varying device therein, a balancing condenser, means comprising a forward-acting circuit operated according to the number of syllables in the signals on the line, means comprising a backwardacting circuit operated according to the time the voltage on the line exceeds a predetermined value, means for charging said condenser constantly according to ratio between the operations of said forward-acting circuit and said backward-acting circuit when signals are on the line, and means controlled according to the charge on said condenser for governing said device to maintainthe signals on the line at substantially constant value.

8. In a signal transmission system, a driver circuit having two normally balanced paths, a transformer having one output secondary winding and two primary windings respectively connected to said paths, a source of alternating current-for energizing each of said paths, said two primary windings being wound oppositely so that no alternating current is supplied to said secondary winding, a source of direct current for jointly energizing said two paths, 'means in said paths for unbalancing said paths when energized with direct current, the path which predominates in energizing the primary secondary winding being determined according to the polarity of said direct current, two three-element cold cathode tubes in circuit with said secondary winding, and means for igniting said cold cathode tubes respectively in synchronism with the currents in said primary windings.

9. In combination, a signal line, two coldcathode tubes, means for operating said tubes respectively by high strength signals and the number of syllables on the line, means for effecting operation of the tubes a substantial amount out of phase with respect to each other, means for weighing the efl'ective operations of said tubes, two enabler cold cathode tubes respectively operated when the detector tubes are operated, means comprising a driver circuit controlled'by said weighing means and operating in phase with the detector which predominates in operating the weighing means, means for controlling the strength of the signals on the line jointly by the driver circuit and the enabler tubes and for determining the direction of gain according to the enabler tube in phase with the driver circuit;

10. In combination, a signal line, two cold cathode tubes, means for insuring operation of saidtubes, a substantial amount out of phase with respect to each other, a syllable circuit connected to said line for operating one of said tubes according to the number of syllables on the line, said syllabic circuit comprising a diode-triode tube, means transmitting signals through the diode-triode when low strength signals are on the line, means for selecting syllabic frequencies from the diode-triode output, a pulser device operated by the syllabic frequency currents, means for effecting operation of the pulser device only on the rising portion of a syllabic impulse and means controlled by the pulser device for supplying spurts of alternating current, said 55 connected to-said line for controlling one of said cold cathode tubes according to the number of syllables on said line, said syllabic circuit comprising a diode-triode, means for transmitting signals through the diode-triode when low strength signals are on the line, means for selecting syllable impulses from the diode-triode output and means for transmitting'spurts of alternating current under control of the syllabic impulses, said last-mentioned means transmitting a fixed spurt of current irrespective of the strength and length of the controlling syllabic impulse, means for operating the other cold cathode tube by high strength signals, means for weighing the effective operation of said tubes, and means controlled by said weighing means to maintain substantially constant volume on said line.

12. In combination, a signal line, control means for'raising and lowering the strength of the signals on the line to hold the signals at constant volume and means comprising a syllabic circuit for governing said control means to raise the gain on the line, said syllabic circuit comprising amplifying and filtering means connected to the line, a diode-triode tube connected to the amplifying filtering means, means for impressing a normal negative bias on the grid of the triode which limits current flow through the triode portion of the diode-triode, means for rectifying signals by the diode to increase the bias on triode grid so that weak signals vary the triode output, a transformer tuned to syllabic frequency connected to the output circuit from the triode, a source of alternating current connected to a resistance pad, means comprising a pulser device for varying the resistance of said pad to permit transmission of spurts of alternating current to operate said control means, said pulser device operating to insure spurts of current of fixed duration irrespective of the strength and duration of the operating syllabic impulse, and means insuring operation of the pulser device only on the rising portion of a syllabic impulse. v

13. In combination, a signal line, means comprising a gain control tube for governing the strength of the signals on the line, two cold cathode detector tubes, means for operating said detector tubes respectively by the syllables and the high strength signals on the line, each of said detector tubes having an ignition circuit and an operating circuit, means for eflecting operation of the detector tubes a substantial amount out of phase with respect to each other, balancing means for weighing the effective operations of said detector tubes, driver means selectively operated by said balancing means according to which of said detector tubes predominates in operating the balancing means and in synchromsm with the predominating detector tube, a gain increaser tube and a gain decreaser tube respectively ignited in synchronism with the operation of said detector tubes, and means for operating said gain control tube to vary the strength of the line signals according to the synchronous operation of the driver means with the gain decreaser tube and the gain increaser tube.

14. In combination, a signal line, means comprising a gain control tube for governing the strength of the signals on the line, two cold cathode detector tubes, means for operating said detector tubes respectively by high strength signals on the line and the syllables of the signals, each oi said detector tubes having an ignition circuit and an operating circuit, a source of alternating current connected to the operating circuits of said detector tubes to effect operation of the tubes by opposite half waves, balancing means or weighing the effective operations of said detector tubes, driver means selectively operated by said balancing means according to which of said detector tubes predominates in operating the balancing means and in synchronism with the predominating detector tube, a gain increaser tube and a gain decreaser tube respectively ignited in synchronism with the currents in the output circuits of the detector tubes, and means for operating said gain control tube to vary the strength of the line signals according to the synchronous operation of the driver means with the gain decreaser tube and the gainincreaser tube.

15. In combination, a signal line, means comprising a gain control tube for governing the strength of the signals on the line, two cold cathode detector tubes, means for operating said detector tubes respectively by high strength signals on the line and the syllables of the signals,

each of said detector tubes having an ignition circuit and an operating circuit, means for effecting operation of the detector tubes a substantial amount out of phase with respect to each other, balancing means for weighing the effective operations of said detector tubes, means comprising a driver circuit selectively operated by said balancing means according to which of said detector tubes predominates in operating the balancing meansand in synchronism with the predominating detector tube, a gain increaser tube and a gain decreaser tube respectively ignited in synchronism with the operation of said detector tubes, means for operating said gain control tube to vary the strength of the line signals according to the synchronous operation of the driver circuit with the gain decreaser tube and the gain increaser tube, and marginal means for preventing operation of the gain control tube until the output from the driver circuit is above a predetermined level.

16. In combination, a signal line, a variolosser on said line for controlling the signal volume, a cold cathode low strength detector tube having an ignition circuit and an operating circuit, a cold cathode high strength detector tube having an ignition circuit and an operating circuit, a syllabic circuit connected to said line before said varistor for energizing the ignition circuit of said low strength detector tube, means for energizing the ignition circuit of the high strength detector tube from said line beyond the vario-losser therein when high strength signals are on the line, a source of alternating current connected to the operating circuits of said detector tubes to efiect operation of the tubes by opposite half waves, means comprising a gain control tube for governing said vario-losser, balancing means for weighing the effective operations of said detector tubes, driver means selectively operated by said balancing means according to which of said detector tubes predominates in operating the balancing means and in synchronism with the predominating detector tube, a gain increaser tube and a gain decreaser tube respectively ignited in synchronism with the currents in the output circuits of the detector tubes, and means for operating said gain control tube to vary the strength of the line signals according to the synchronous operation of the driver means with the gain decreaser tube and the gain increaser tube.

BJORN G. BJORNSON. 

